THE mother of the Boston Marathon bombing suspects insists that her sons are innocent and that she is not a terrorist.

But Zubeidat Tsarnaeva is drawing increased attention after federal officials say Russian authorities intercepted her phone calls, including one in which she vaguely discussed jihad with her elder son.

In another, she was recorded talking to someone in southern Russia who is under FBI investigation in an unrelated case.

In photos of her as a younger woman, Mrs Tsarnaeva wears a low-cut blouse and has her hair teased like a 1980s rock star. After she arrived in the US from Russia in 2002, she went to beauty school and did facials at a suburban day spa.

But in recent years, people noticed a change. She began wearing a hijab and cited conspiracy theories about 9/11 being a plot against Muslims.

She insists there is no mystery and that she is just someone who found a deeper spirituality and fiercely defends her sons - Tamerlan, who was killed in the gunfight with police, and Dzhokhar, who was wounded and captured.

"It's all lies and hypocrisy," she said. "I'm sick and tired of all this nonsense that they make up about me and my children. People know me as a regular person, and I've never been mixed up in any criminal intentions, especially any linked to terrorism."

At a news conference in Dagestan with her ex-husband Anzor last week, she appeared overwhelmed with grief one moment, defiant the next. "They already are talking about that we are terrorists, I am terrorist," she said. "They already want me, him and all of us to look (like) terrorists."

Amid the scrutiny, she and ex-husband Anzor Tsarnaev say they have put off the idea of any trip to the US to reclaim their elder son's body or try to visit Dzhokhar in jail.

It is unclear whether religious differences fueled tension in their family. Anzor and Zubeidat divorced in 2011.

About the same time, there was a brief FBI investigation into Tamerlan Tsarnaev, prompted by a tip from Russia's security service.